Method of retroperitoneal lateral insertion of spinal implants

ABSTRACT

A method is disclosed for introducing a spinal disc implant into an intervertebral space of a subject. The subject is placed in a lateral position, and the anterior face of the spinal disc intervertebral space is accessed, between the L5 and S1 vertebrae, from an anterior and lateral retroperitoneal approach. An operative corridor to the anterior face of the spinal disc space is established by introducing a retractor instrument anterolaterally to the spinal disc space between the anterior superior iliac spine and the anterior inferior iliac spine. The damaged spinal disc contents are removed from the intervertebral space through the operative corridor, and the implant is advanced into the intervertebral space at an oblique angle and pivoted to position the implant substantially laterally within the intervertebral space. Elongated retractor and insertion instruments, as well as a modified disc implant, are also disclosed for carrying out the method.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.13/239,014 entitled “METHOD OF RETROPERITONEAL LATERAL INSERTION OFSPINAL IMPLANTS” filed on Sep. 21, 2011, which is a continuation of U.S.patent application Ser. No. 13/133,909 entitled “MINIMALLY-INVASIVERETROPERITONEAL LATERAL APPROACH FOR SPINAL SURGERY” filed on Jun. 9,2011, which was the National Stage of International Application No.PCT/US2009/069476, filed Dec. 23, 2009, which claims priority to U.S.Provisional Application No. 61/178,315, filed May 14, 2009, and U.S.Provisional Patent Application No. 61/140,926, filed Dec. 26, 2008, allof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Spinal surgery methods and devices are disclosed for repairing damagedor deteriorated vertebrae at the lower lumbar levels, such as in theL5-S1 intervertebral space.

2. Description of the Relevant Art

The vertebral column is the central pillar of the body. It is agenerally flexible column that bears tensile and compressive loads,permits bending motions, and provides an attachment site for ribs,muscles and other structures. The vertebral column includes irregularbones called vertebrae that are separated by fibrocartilaginousstructures known as intervertebral discs. There are seven vertebral,twelve thoracic, five lumbar, five sacral, and four coccygeal vertebrae.A typical vertebra consists of a rounded anterior body and a posteriorvertebral arch that together form a protective structure around thevertebral canal that contains the spinal cord.

The intervertebral discs can be damaged or undergo degeneration, whichoften results in painful and sometimes debilitating nerve impingementsyndromes. It is sometimes necessary to surgically replace the nativedisc with prosthetic disc implants to relieve the pain, restore thefunctional mechanics of the vertebral column, and promote fusion betweenadjacent vertebral bodies. Procedures such as total disc arthroplasty(disc replacement) have used a direct anterior approach orthogonal tothe midline of the vertebral body, but such procedures requireunfettered anterior spinal exposure for precise midline placement of theprosthetic disc. The major vascular structures that run along theanterior spine must be mobilized to achieve this exposure, whichtypically requires the assistance of a vascular surgeon. The procedurealso causes significant surgical disruption of the anterior annularelement around the disc.

Bertagnoli has described an anterolateral transpsoatic approach (ALPA)for implantation of prosthetic disc replacement devices. The patient ispositioned in a supine position on the operating table, with the arms inabduction. The target disc level is localized through bi-planarfluoroscopy, and an inflatable bladder is placed beneath the level ofinterest to permit additional lordosis. An anterolateral incision ismade on the left side for access to lumbar intervertebral spaces, whilethe incision is made on the right side for access to L5-S1. The fasciaof the external oblique muscle is opened along the direction of itsfibers and the muscle is split. The retroperitoneal space is entered andthe peritoneal sac mobilized away from the overlying fascia to developan operative pathway along the anterior aspect of the psoas muscle tothe lateral aspect of the intervertebral space. The target zone forannulotomy is from the one o'clock to three o'clock position above theL5-S1 level, which leaves the anterior longitudinal ligament intact andavoids mobilizing the iliac vessels. At the L5-S1 level the targetannulotomy zone is from the eight o'clock to ten o'clock position withmobilization of the iliac vessel toward the midline. Injury to the leftiliac vessel is an unfortunate complication of such procedures.Additional information about anterolateral approaches to spinal surgeryat the L4-L5 level is found in Bertognali et al, U.S. Pat. No.7,326,216.

A minimally invasive procedure promoted by Nuvasive, Inc. uses a directlateral, retroperitoneal approach to access the intervertebral discsabove the L5-S1 level with minimal muscular disruption. The patient isplaced in a lateral decubitus position and the direct lateral incisionis made in the axillary line. Another incision is made posterior to thelateral border of the erector spinae muscle, and finger dissection isconducted through this opening to the retroperitoneal space. The indexfinger of the surgeon sweeps the peritoneum anteriorly and palpates thepsoas muscle. A dilator instrument is then introduced through the directlateral incision and the index finger then guides the dilator instrumentto the psoas muscle. The fibers of the psoas muscle are then split usingblunt dissection and EMG monitoring to minimize damage to the nerves ofthe lumbar plexus that run through the posterior psoas muscle. A tissuedistraction and tissue retraction assembly are then used to helpestablish an operative corridor to the direct lateral aspect of theintervertebral space at about the 3 o'clock position, as shown in U.S.Pat. No. 7,207,949. The direct lateral retroperitoneal approach to theL5-S1 space has not been possible because the anterior superior iliacspine obstructs a direct lateral approach to the L5-S1 intervertebralspace. Hence approaches to the L5-S1 space typically use a standardanterior approach. For a laterally positioned patient, an extremelylarge sigmoidal incision has been required, with subsequent reflectionof all the overlying musculature to expose the L5-S1 space.

It would therefore be useful to provide a minimally invasive approach tothe L5-S1 space that minimizes injury to the blood vessels and nervesaround the vertebral bodies. It would also be helpful to perform such aprocedure in a manner that minimizes retroperitoneal scarring and damageto other body structures. Minimally invasive surgical approaches to theintervertebral spaces in the past have also been limited by the need toinsert the prosthetic disc implant either into the front portion,posterior portion, or the side of the disc space to achieve stableplacement of the prosthetic implant. It would therefore be useful tohave a procedure that could avoid such a limitation at any vertebrallevel.

SUMMARY OF THE INVENTION

The inventor has found it is advantageous to provide a method, deviceand system that permit an angle between a disc implant and insertioninstrument to be altered without removing the implant from theintervertebral space. This new surgical approach also removes the nativedisc contents from a generally lateral direction, which permits theperitoneal contents to fall out of the surgical field, while also takingadvantage of the mechanics of anterior interbody surgery.

Disclosed methods, devices and systems are suitable for performing aminimally-invasive procedure for accessing the intervertebral spacealong an oblique pathway with an insertion instrument that holds a discimplant, and reorienting the angular relationship between instrument andimplant while the implant is inside the body (for example at or withinthe disc space). In some disclosed embodiments, a prosthetic discimplant is inserted diagonally within the disc space, and the implant isthen pivoted to a medial-lateral orientation within the disc space. Theinvention is particularly useful for accessing the L5-S1 intervertebralspace along an anterolateral pathway to the anterior aspect of thespine, placing a prosthetic disc implant diagonally within theintervertebral space, and pivoting the implant within the disc space.However the method can also be used at other vertebral levels. In oneembodiment, the oblique pathway has a caudal or cephalad-directedcomponent, and the implant can be repositioned into a transverseanatomic plane through the intervertebral space.

In one embodiment, an implant is positioned in the intervertebral discspace of a laterally positioned subject by accessing the anterior faceof the spinal disc intervertebral space, between the L5 and S1vertebrae, from an anterolateral retroperitoneal approach. An obliqueoperative corridor is then established to the anterior face of thespinal disc space by introducing a retractor instrument anterolaterallyto the spinal disc space, for example anterior to the anterior superioriliac spine, and in some instances between the level of the anteriorsuperior iliac spine and the anterior inferior iliac spine. The spinaldisc contents are removed from the intervertebral space through theoperative corridor, and an elongated implant is introduced through theoperative corridor into the intervertebral space diagonally (at anangle). The elongated implant is then pivoted within the intervertebralspace to eventually position the implant substantially medial-laterallywithin the intervertebral space and achieve midline symmetricdistribution of the mechanical load on the implant. The ability to pivotthe implant within the intervertebral space permits the elongatedimplant to be generally aligned with the insertion instrument andadvanced into the body through a relatively narrow operative corridor,then turned to its final position within the intervertebral space.

In a disclosed embodiment, the retractor instrument includes a proximalhandle portion and a distal retractor blade portion that carriesopposing ipsilateral and contralateral vascular retractor blades thatare placed between the right and left iliac vessels and moved apart fromone another to retract the right and left iliac vessels away from theanterior face of the spinal disc intervertebral space. A particularexample of the retractor instrument has an ipsilateral arm on which theipsilateral blade is mounted and a contralateral arm on which thecontralateral blade is mounted. The retractor blades are placed betweenthe right and left iliac vessels to move them away from one another toexpose the anterior surface of the spine as the ipsilateral andcontralateral arms of the retractor instrument move the retractor bladesapart. For example, the blades of the retractor instrument arepositioned at the anterior face of the vertebral body adjacent theanterior longitudinal ligament, and the retractor blades are spread toexpose an area from about the 10 o'clock to 2 o'clock position of thevertebral body.

The elongated implant may be advanced into the intervertebral spacethrough the operative corridor defined by the arms of the retractorinstrument by securing the implant to a distal end of an elongated rigidintroducer instrument and advancing the implant on the introducerinstrument through the operative corridor to the anterior face of theintervertebral space at an oblique angle so that the implant enters thedisc space diagonally. The angle between the implant and the introduceris then selectively changed to pivot the implant in one or moresubsequent steps into the medial-lateral position for symmetric midlineplacement within the intervertebral space. In some embodiments theintroducer instrument has a distal docking element that selectivelydocks with an interface element of the implant in a series ofpreselected positions to alter the angle between the implant and theintroducer instrument. For example, the docking element is a pluralityof docking pins on the tip of the introducer element, and the interfaceelement is a corresponding series of docking holes that cooperativelymate to hold the implant in preselected angular orientations to theintroducer instrument.

In some disclosed embodiments, the implant is an elongated elastomericmember that has a top bearing face, a bottom bearing face, a front face,a rear face, an ipsilateral face and a contralateral face. The rear faceof the implant may be substantially flat. The contralateral face of theimplant may be rounded (particularly at its corners that adjoin thefront and rear faces) to minimize trauma induced by advancing theimplant diagonally into the intervertebral space at the oblique angle,and using the ipsilateral face to function as an impact hinge or pivotpoint as the implant is moved in one or more realignments from theoblique to medial-lateral orientation. The ipsilateral end of theimplant may have a pivot axis and an interface element, such as multiplepairs of spaced docking holes arranged on a curved surface that extendspartially circumferentially around the pivot axis. The selected pairs ofspaced docking holes are positioned to mate with the docking element ofthe introducer instrument, such as a pair of docking pins that extendfrom a distal tip of the introducer instrument.

In some embodiments the implant tapers in height from its front face torear face, and/or medially to laterally, and it may be a partiallyhollow member in which the top face and bottom face are substantiallyopen and separated by an internal divider wall that extends from thefront face to the rear face to form a contralateral and ipsilateralwindow though the implant to promote the growth of bone within theimplant. In some disclosed embodiments, the implant is a slightlycompressible member in which the front face is convex and theipsilateral face includes the interface element that mates with thedocking element. The external surfaces of the implant (such as the topand bottom faces of the implant) have protuberances that helpfrictionally engage the implant to adjoining vertebral bodies, and alsopromote bone growth into the implant. The protuberances may have avariety of shapes, such as grooves or corrugations, but afrustopyramidal protuberance is believed to be particularly suitable.

The retractor instrument may also take a variety of forms, but certaindisclosed embodiments have an ipsilateral arm that is shorter than thecontralateral arm. A retractor blade on the ipsilateral arm thereforeextends a shorter distance from the handle than the retractor blade onthe contralateral arm. This asymmetric arrangement permits the retractorinstrument to be advanced diagonally through the body from ananterolateral entrance point through the abdominal wall to the anterioraspect of the vertebral body. Since the contralateral arm is longer thanthe ipsilateral arm, the retractor blades at the anterior vertebral bodyspan the anterior face of the vertebral body, for example from the 10o'clock to 2 o'clock positions. The retractor blades may be curvedoutwardly from a longitudinal axis of the retractor instrument to helpminimize damage to the blood vessels as they are retracted. A thin shimwith a tapered tip may be inserted into the intervertebral space andmounted to the ipsilateral blade to retain the instrument in its desiredangular orientation and distract adjacent vertebral bodies (such as L5and S1) apart from one another during the procedure. The shim curvesinwardly into the disc space, toward the midline of the body, away fromthe ipsilateral retractor blade, and toward a longitudinal axis of theretractor instrument. The shim has a height sufficient to maintain theadjacent vertebral bodies spaced from one another while a trial spacerand subsequent disc implant are pivoted into place within the discspace. The present disclosure also includes a system for positioning animplant in an intervertebral space of a subject. In certain disclosedembodiments, the system includes the retractor instrument forestablishing an operative corridor to the anterior face of theintervertebral space. The retractor instrument has a proximal handleportion and a distal retractor blade portion that includes opposingipsilateral and contralateral arms that are movable toward and away fromone another to define a portion of the operative corridor therebetween.In certain embodiments, the ipsilateral retractor blade is carried bythe ipsilateral arm, and a contralateral vascular retractor blade iscarried by the contralateral arm. The contralateral arm and blade arelonger than the ipsilateral arm and blade so that the retractorinstrument can be introduced at an oblique angle with the two retractorblades spaced apart on the anterior aspect of the vertebral body.

The system also includes the introducer instrument for advancing anelongated prosthetic spinal disc implant between the arms and blades ofthe retractor instrument to the intervertebral space at an oblique angleso that the implant enters the intervertebral space diagonally. Theintroducer instrument is capable of pivoting the implant in theintervertebral space, for example by connecting docking pins on a tip ofthe introducer instrument to different sets of corresponding dockingholes on the implant. The docking pins selectively mate with thedifferent sets of docking holes on the implant to maintain the implantat different fixed angles to the introducer instrument. By mating thedocking pins with different docking holes, the implant can be pivotedwithin the intervertebral space to move it from its initial diagonalorientation to a medial-lateral orientation generally symmetric withrespect to the axis of the vertebral column. In certain embodiments, thesystem also includes the implant which has a top bearing face, a bottombearing face, a front face, a rear face, an ipsilateral face and acontralateral face. The implant's contralateral face may be rounded tominimize trauma induced by advancing the implant diagonally into theintervertebral space and pivoting it around a pivot axis within theintervertebral space. The implant has an interface element for couplingwith the introducer instrument and pivoting the implant within the discspace. For example, the interface element includes multiple pairs ofspaced docking holes arranged on a curved surface that extends partiallycircumferentially around the pivot axis, and selected pairs of spaceddocking holes are positioned to mate with the docking element of theintroducer instrument. In certain disclosed embodiments, the implanttapers in height from the front face to the rear face. The implant mayalso be a partially hollow member in which the top face and bottom faceare substantially open and may be separated by an internal divider wallthat extends from the front face to the rear face to define theipsilateral and contralateral windows therebetween for promoting tissuegrowth within the implant.

Another aspect of the invention is the prosthetic implant itself, theretractor itself, and the introducer element itself.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become apparent to thoseskilled in the art with the benefit of the following detaileddescription of embodiments and upon reference to the accompanyingdrawings in which:

FIG. 1A illustrates a patient positioned in a right lateral decubitisposition for minimally-invasive spinal surgery using a retroperitonealapproach;

FIG. 1B is a schematic top view illustrating the anatomy of the L5vertebra;

FIG. 1C is a schematic perspective view of the human body illustratingseveral anatomic reference planes;

FIG. 2A is a schematic cross-sectional view of the abdomen at the levelof the L5-S1 intervertebral space illustrating the left anterolateraldisplacement of the peritoneum and the right anterolateral introductionof a dilator through an incision toward the L5-S1 space under theguidance of a surgeon's finger introduced through a lateral incision;

FIG. 2B is an isolated perspective view illustrating the components anduse of an initial distraction assembly that includes a K-wire, aninitial dilating cannula with handle, and a split-dilator housed withinthe initial dilating cannula;

FIG. 2C is an isolated perspective view illustrating the K-wire andsplit-dilator of the initial distraction assembly with the initialdilating cannula and handle removed;

FIG. 3A is a view similar to FIG. 2A, but showing introduction of aminimally invasive retractor instrument through the right anterolateralincision, and its positioning at the L5-S1 intervertebral space with theright and left iliac vessels retracted away from the anterior spine;

FIG. 3B is an isolated schematic end view of the retractor blades on theretraction instrument, illustrating the greater curvature of the shorterretraction blade;

FIG. 4A is a front elevation view of a shim for placement on theipsilateral blade of the retractor instrument;

FIG. 4B is a side view of the shim of FIG. 4A;

FIG. 4C is a top view of the shim of FIGS. 4A and 4B;

FIG. 5A is a perspective fragmentary view of the pelvis and thesacro-lumbar segment of the spinal column illustrating the bifurcationof the iliac vasculature along the anterior aspect of the spinal column;

FIG. 5B is a front view of FIG. 5A with the iliac vessels retracted toexpose the L5-S1 disc space;

FIG. 6 is a perspective view of an introducer instrument for guiding animplant to a spinal disc space, showing the implant connected to theintroducer instrument for movement about a pivot axis;

FIG. 7 is an isolated perspective view of the introducer instrument;

FIG. 8 is an enlarged, fragmentary view of the tip of the introducerinstrument of FIG. 7 illustrating the instrument interface of theimplant, and showing the pins on the distal tip of the instrument forconnection to positioning holes on the implant;

FIG. 9 is an enlarged, fragmentary view of the implant held in a fixedangular position relative to the introducer element by the pins of theinstrument interface locked into a preselected set of positioning holeson the implant;

FIG. 10A is a perspective view of a first embodiment of the implant,showing the implant interface surface in which pairs of pin receivingholes are arranged at different angles around the interface surface tohold the implant at variable fixed angles relative to the longitudinalaxis of the introducer instrument;

FIG. 10B is an end view of the implant of FIG. 10A, illustrating atapered height of the implant;

FIG. 11A is a top view of an embodiment of an implant;

FIG. 11B is a side view of an embodiment of the implant of FIG. 11A;

FIG. 11C is an end view of an embodiment of the implant of FIG. 11A;

FIG. 12 is a perspective view of a second embodiment of the implant;

FIG. 13 is a schematic top perspective view of the pelvis with aretractor instrument introduced obliquely into the subject's body alongan anterolateral operative trajectory, and with the introducerinstrument advanced through the operative corridor defined by theretractor instrument. A trial spacer is attached to the distal end ofthe introducer instrument for introduction diagonally into the L5-S1intervertebral space;

FIG. 14A is an enlarged top view of the L5-S1 disc space shown in FIG.13, illustrating the rounded contralateral face of the trial spacerimpacting the far lateral aspect of the apophyseal ring;

FIG. 14B is a view similar to FIG. 14A, but illustrating adjustment ofthe angle between the introducer instrument and the body of the trialspacer by repositioning the pins on the tip of the instrument in adifferent set of pin receiving holes on the trial spacer;

FIG. 14C is a view similar to FIG. 14C, but illustrating progressivereorientation of the trial spacer in a generally medial-lateralorientation within the intervertebral space;

FIG. 15 is a view similar to FIG. 13, but showing a subsequent step ofthe procedure in which the introducer instrument has advanced an implantto the disc space;

FIGS. 16A, 16B and 16C are top views of the L5-S1 disc space,illustrating progressive reorientation of the implant within the discspace by repositioning of the pins on the tip of the introducerinstrument in different sets of pin receiving holes on the implant;

FIG. 17 is an enlarged top view of the L5-S1 disc space illustrating theimplant in position within the disc space;

FIG. 18A is a front elevation view of a shim for placement on theipsilateral blade of the retractor instrument;

FIG. 18B is a side view of the shim of FIG. 18A;

FIG. 18C is a top view of the shim of FIGS. 4A and 4B;

FIG. 19A is a perspective view of an embodiment of an implant;

FIG. 19B is a side view of an embodiment of the implant of FIG. 19A;

FIG. 19C is an end view of an embodiment of the implant of FIG. 19A;

FIG. 20 is a top view of the L5-S1 disc space, illustrating orientationof the implant of FIG. 11A within a disc space;

FIG. 21 is a perspective view of a portion of a retraction instrumentwith a pair of blades provided at a distal end;

FIG. 22 is a top view of the retraction instrument of FIG. 21, showing amechanism for moving the retractor blades;

FIG. 23A is a perspective view of a blade for use with a retractioninstrument;

FIG. 23B is a rear view of the blade of FIG. 23A; and

FIG. 23C is a top view of the blade of FIG. 23A.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood, however, that thedrawings and detailed description thereto are not intended to limit theinvention to the particular form disclosed, but to the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It is to be understood the present invention is not limited toparticular devices or methods, which may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include singular and pluralreferents unless the content clearly dictates otherwise. Furthermore,the word “may” is used throughout this application in a permissive sense(i.e., having the potential to, being able to), not in a mandatory sense(i.e., must). The term “include,” and derivations thereof, mean“including, but not limited to.” The term “coupled” means directly orindirectly connected.

Embodiments of the invention are disclosed herein for accessing anintervertebral space, such as the L5-S1 space, and implanting aprosthetic disc implant within that space. The disclosed devices,methods and systems are suitable for use in a minimally invasiveprocedure for repairing degenerated or otherwise injured intervertebraldiscs.

General Overview of the Surgical Procedure

The method generally includes initially accessing the intervertebralspace using a retroperitoneal lateral approach. Then, with afinger-directed dilator or other suitable instrument, the distalretroperitoneum is swept anteriorly to expose an eventual channel to adirect approach to L5-S1. In most people, the direct approach to L5-S1is anterior to the anterior superior iliac spine, or between theanterior superior iliac spine and the anterior inferior iliac spine. Anincision is then made to open this channel, and blunt dilators aredirected in an oblique direction directly to the mid-anterior aspect ofL5-S1, for example between the 10 o'clock and 2 o'clock position.Fluoroscopic guidance may be used in accordance with known techniques toassist in advancing and positioning the dilators.

A retractor is then advanced over the dilators. In certain embodiments,the blades of the retractor are translucent so that the retractedcontents can be seen through the blades. In contrast to existingretractors used in minimally invasive spinal surgery, the blades areshaped so that the curvature of the retractor blades conforms to theunique shape of the anatomy for the approach described herein, and isparticularly suitable for use in this portion of the spine. For example,the ipsilateral blade may be shorter than the contralateral blade, andthe ipsilateral blade may be more arcuate with a steeper curve ascompared to the less curved, straighter contralateral blade. In oneembodiment, the blades can accommodate a xenon light source forvisualization in the cavity.

Once the retraction blades are advanced to the anterior aspect of thespine (for example between the 10 o'clock and 2 o'clock positions at theL5-S1 intervertebral space), the retractor blades are positioned belowthe iliac bifurcation between the right and left iliac vessels. Theretractor blades are moved apart to increase exposure of the anteriorvertebral column. A docking shim that is angled away from theipsilateral blade and toward the disk space is placed in theintervertebral space to secure the retractor in position and maintaindistraction of the vertebral bodies. If the small middle sacral arteryis viewable in the midline, the surgeon may choose to ligate orelectrocauterize this small vessel.

The procedure provides a relatively large window within which adiscectomy and reconstruction can be carried out. The tools used for thediscectomy may be slightly angled (relative to tools used for existingtechniques) to maximize disc removal from an oblique direction. Trialspacers and final disc implants have a unique design suited to thetrajectory of the implantation, as described in greater detail below.Radiopaque markers may be included on the trial spacers and implants(for example at its corners) to enable the structures to be visualizedunder fluoroscopy.

One or more trial spacers are then introduced into the evacuated discspace to help select an appropriate size implant. During introduction ofthe trial spacer or final implant, the initial insertion trajectory isoblique, resulting in diagonal entry of the trial spacer into disc spacewith impaction of the contralateral face of the implant or trial spacerto the far lateral aspect of the apophyseal rings (for example ofL5-S1). The angle of impaction is then reoriented so that the portion ofthe trial spacer or implant that is present in the more anterior portionof the intervertebral space is impacted posteriorly on the apophysealring by using the contralateral side as a swivel point. Underfluoroscopic control, final seating of the implant or trial spacer isachieved. Once the final implant is in place, retraction is slowlyreleased by allowing the retraction blades to move toward one another tocheck for any residual bleeding. The retractor is then slowly removed sothat the skin closure of the percutaneous incision can be carried out.

This general summary of the procedure is illustrated in more detail inthe following sections of this specification.

Positioning the Patient and Relevant Spinal Anatomy

As shown in FIG. 1A, a patient 20 is placed in a direct right lateraldecubitis position with the patient's right side down on an operatingtable 22 and the left side up. A bolster pillow 24 is placed at thewaist of patient 20 to bend the body at that point, which elevates andtilts the pelvis 26 of patient 20. Pelvis 26 is schematically shown inFIGS. 1, 5A and 5B to include an ileum 28, with an iliac crest 30,anterior superior iliac spine 32, and anterior inferior iliac spine 34.A notch 36 (FIGS. 5A and 5B) is formed between the superior and inferioriliac spines 32, 34. The spinal anatomy is schematically illustrated inFIG. 1A, wherein the sacrum 38 is shown connected to the L5 vertebra 40.Higher levels of lumbar and thoracic vertebrae are shown superior to theL5 disc. The anatomy of the L5 vertebra is illustrated in more detail inFIG. 1B, wherein the vertebra includes an anterior vertebral body 42 anda posterior vertebral arch 44 that cooperatively define spinal foramen46. Vertebral body 42 includes a circumferential apophyseal ring 48,while vertebral arch 44 includes a spinous process 50, right transverseprocess 52 and left transverse process 54. Positions around vertebralbody 42 can be designated arbitrarily by hours of the clock, withanterior-most position 56 designated the twelve o'clock position. Hencean anterior face of vertebral body 42 is designated herein as the face58 that extends from about the ten o'clock position 60 to the twoo'clock position 62. The axis of the vertebral column is locatedgenerally at the center of vertebral body 42.

To clarify some of the terms in this specification, the anatomic planesof the body in the standard anatomical position are shown in FIG. 1C. Ingeneral anatomic terminology, “superior” means closer to the head,“posterior” means closer to the posterior surface of the body,“anterior” means closer to the anterior surface of the body, “cephalad”means toward the head, “caudad” means toward the feet. The anatomicreference planes in FIG. 1C are the “coronal plane” that separates thebody into anterior and posterior halves, and the “median plane” thatseparates the body into right and left parts. A transverse plane isshown, which is any plane that is perpendicular to the coronal andmedian planes; multiple transverse planes exist at different levels ofthe body. With reference to the coordinate planes of FIG. 1C, the “noon”position is on the front of the body along the A-P (anterior-posterior)line at which the median plane intersects a transverse plane. The threeand six o'clock positions are along the L-M (lateral-medial) line at theintersection of the transverse and coronal planes.

An “oblique plane” is any plane that is at an angle (not within orparallel) to any one of the coronal, median or transverse planes. Hencean operative corridor is “oblique” if it is an oblique plane. An obliqueangle can lie in one of the illustrated coronal, median or transverseplanes, be parallel to one or two of those planes, or be outside of (andnot parallel) to all three of them. For instance, an oblique pathway P1to an intervertebral space can extend in a transverse plane at anon-zero angle to the median plane. Alternatively, an oblique pathway P2can extend at a non-zero angle to the transverse, coronal and medianplanes.

Additional pertinent anatomy at the anterior aspect of the spine isillustrated in FIGS. 5A and 5B, which shows the aortic bifurcation 64into the right and left common iliac arteries 66, 68, each of whichdivides into an external iliac artery 66 a, 68 a and an internal iliacartery 66 b, 68 b. Accompanying common iliac veins 67, 69 are also shownin FIG. 5A. The descending aortic artery, bifurcation 64, and thebifurcated iliac vessels are at the anterior face of the vertebralbodies, and have complicated surgical approaches that attempt to accessthe anterior vertebral body to repair a damaged spinal disc. The L5-S1intervertebral space 70 is shown in FIG. 5A without retraction of theiliac vessels, and in FIG. 5B with retraction of the iliac vessels toexpose L5-S1 intervertebral space 70.

Additional pertinent perispinal anatomy is shown in FIGS. 2A and 3A,wherein right and left common iliac arteries 66, 68 and veins 67, 69 areshown in their normal anatomic position on the anterior aspect of thespine. The nucleus pulposus 72 of the L5-S1 intervertebral disc isillustrated, as are the right and left psoas muscles 74, 76, the rightand left erector spinae muscles 78, 80 and the right and lefttransversospinalis muscles 82, 84. The peritoneum 86, which is normallyadjacent and adherent to the retroperitoneal structures, is shown inFIGS. 2A and 3A after it has been moved anteriorly and separated fromthe retroperitoneal structures on the right side of the body to clear anoperative pathway to the L5-S1 intervertebral space.

Access to Retroperitoneal Space and Establishing Operative Corridor toIntervertebral Space

The surgeon palpates the subject to locate the position of the anteriorsuperior iliac spine 32, and an initial incision 90 (FIG. 1) is made atthis point in the mid-axillary line, as in a standard retroperitonealapproach. As shown in FIG. 2A, blunt finger dissection is directedcaudally in the retroperitoneal plane to connect to a point that isparallel the L5-S1 disc space, just anterior to ileum 28. The surgeon'sfinger 94 sweeps peritoneum 86 anteriorly, moving it away from the ileum28 and the retroperitoneal structures in the right side of the abdominalcavity. A second skin incision 92 (FIGS. 1A and 2A) is then madeinferior to first incision 90. Second incision 92 is anterior to firstincision 90, between the anterior axially line and the sheath of therectus abdominis muscle, and is approximately 3-5 cm in length. Secondincision 92 is made at the level of the L5-S1 disc space, which isdetermined fluoroscopically prior to making the incision. FIG. 2Billustrates an initial access assembly 100 for accessing the targetedintervertebral space, such as the L5-S1 intervertebral space. Although aparticular device and method are described for accessing the L5-S1intervertebral space, the disclosed invention is not limited to use ofthis particular device and method. The term “accessing” theintervertebral space or its face is meant to broadly include any deviceand/or method for establishing a pathway from a surface incision to thedisc space or its face. Illustrated access assembly 100 includes aK-wire 102, an initial dilating cannula 104 with handle 106, and asplit-dilator 108 housed within the initial dilating cannula 104. Theentire assembly 100 is advanced under fluoroscopic guidance through thetissue towards the surgical target site (i.e. annulus). This may beaccomplished using a nerve detection and/or direction device asdescribed in U.S. Pat. No. 7,207,949, although the nerve detectioncapability is not necessary. Initial dilating assembly 100 is advanceduntil the distal ends of split-dilator 108 and initial dilator 104 arepositioned within the disc space. The initial dilator 104 and handle 106are then removed (FIG. 2C) to leave split-dilator 108 and K-wire 102 inplace. Split-dilator 108 is thereafter split such that the respectivehalves 108 a, 108 b are separated from one another to distract tissue ina generally cephalad-caudal fashion relative to the target site asdescribed in more detail in U.S. Pat. No. 7,207,949. Split dilator 108may thereafter be relaxed (allowing the dilator halves 108 a, 108 b tocome together) and rotated approximately 90 degrees such that thedilator halves 108 a, 108 b are disposed in a transverse anatomic plane.Once rotated in this manner, the dilator halves 108 a, 108 b are againseparated to distract tissue in the transverse plane. Each dilator half108 a, 108 b may be provided with one or more electrodes (preferably attheir distal regions) equipped for use with a nerve surveillance system,such as, by way of example, the Neuro Vision System, although the nervemonitors are optional.

Progressively larger dilators (not shown) may be used to furtherestablish the operative pathway. The dilators are labeled with depthmarkings to help assure insertion of the successive dilators to theappropriate depth. The dilators are introduced obliquely into the bodyalong a diagonal pathway from incision 92 to the anterior aspect of thespine to enter the intervertebral space between the twelve o'clock andtwo o'clock positions. The particularly illustrated pathway is generallyin a transverse plane at the level of L5-S1, but at an angle to (andbetween) the coronal and median planes (for example in the direction ofthe pathway P1 in FIG. 1C). However, the pathway can also be at an angleto the transverse plane as well (for example, at the same angle aspathway P2 in FIG. 1C). The dilator pathway helps determine the eventualoperative corridor that is established by placement of retractioninstrument 110. However, in some embodiments, the retraction instrument110 can itself establish the operative corridor without the initial useof the dilators.

In the illustrated embodiment, one of more of the dilators is left inplace to serve as a guide for insertion of a retractor instrument 110(FIG. 3A). Retraction instrument 110 includes a proximal handle portion112 and a distal retractor blade portion 114 that includes opposingcontralateral retraction arm 116 and ipsilateral retraction arm 118,which respectively carry a terminal contralateral retraction blade 120and ipsilateral retraction blade 122. Each of blades 120, 122 is curvedlongitudinally away from the axis of elongated retractor instrument 110(FIG. 3A), and is additionally curved radially (FIG. 3B). As shown inFIGS. 3A and 3B, ipsilateral retraction blade 122 is shorter and has agreater cross-sectional (radial) curvature than contralateral retractionblade 120. In addition, ipsilateral blade 122 has a greater longitudinalcurvature than contralateral blade 120.

A pair of angled extension members 117, 119 can extend from handleportion 112 to improve the access angle provided by the retractorinstrument. Conventional retraction instruments are not well suited forapproaches that are not directly lateral to an implantation site. Theincreased distance from the handle to the blades and the change in angleprovided by extension members 117, 119 improve access to theimplantation sites for the methods described herein.

In particular, extension members 117, 119 can extend from handle portion112 such that they are substantially parallel to one another and form anangle of between about 45 and 80 degrees from a plane formed by asurface of handle portion 112 to which extension members abut and fromwhich extension members extend. As shown in FIG. 22, extension member119 is preferably shorter than extension member 117. If desired, acentral angled extension member 121 can be provided between extensionmembers 117, 119 to receive another blade member. Arms 116, 118 (FIG.3A) are coupled to extension members 117, 119, respectively.

Arms 116, 118 and their respective retraction blades 120, 122 can bemoved toward and away from one another by the movement of handles 124,126, generally as shown in U.S. Pat. No. 7,207,949. Preferably, handles124, 126 are coupled to a gear mechanism that converts the movement ofthe handles toward each other into linear movement of retraction arms116, 118 away from one another to widen the distance between those armswithout rotating them. The distance between handles 124, 126 can beadjusted and fixed by rotation of knobs 134, 136.

The retraction instrument 110 is placed in cannulated fashion over thedilators with the shorter ipsilateral arm/retraction blade on theipsilateral side of the operative corridor. Retraction instrument 110 isslightly opened by moving handles 124, 126 toward one another so thatopposing retraction arms 116, 118 move farther apart without rotation ofthe retraction arms. A standard xenon light source is carried by theinstrument, and it is used for visualization of the anatomy at thedistal tip of the instrument to position the retractor blades betweenthe bifurcation of the right and left common iliac arteries and veins.The foot of ipsilateral blade 122 is placed beneath the ipsilateralvasculature (the right side for the approach illustrated in FIG. 3A) andthe foot of contralateral blade 120 is placed under the contralateralvasculature (the left side for the approach illustrated in FIG. 3A).Handles 124, 126 are then moved closer together and fixed in position tomove retraction arms 116, 118 away from one another and create surgicalexposure of the anterior spine by moving ipsilateral vessels 66, 67posteriorly and laterally with ipsilateral blade 122, and by movingcontralateral vessels 68, 69 anteriorly and laterally with contralateralblade 120. Handles 124, 126 can be moved and fixed in differentpositions by rotation of knobs 134, 136.

FIGS. 5A and 5B illustrate retraction of the iliac vasculature to exposethe L5-S1 intervertebral space; FIG. 5B also shows the trajectory alongwhich retraction instrument 110 may be advanced. FIG. 5A shows the iliacvasculature running along the anterior spine near the front of the L5-S1intervertebral space 70. FIG. 5B illustrates the iliac vessels retractedaway from the anterior face of the spine by the retractor instrument 110(not shown). A trajectory along which retractor instrument 110 may beintroduced is shown by arrow 128 in FIG. 5B. The illustrated trajectoryis from anterolateral incision 92 through the region of notch 36 betweenanterior superior iliac spine 32 and anterior inferior iliac spine 34.This trajectory contrasts with trajectory 130 (dotted line in FIG. 5B)taken by prior minimally invasive direct lateral surgeries for the L4-L5disc space from the axillary line.

According to one aspect of the invention, once satisfactory ipsilateralvascular retraction is achieved, a shim 132 (FIGS. 3A and 4A, 4B, 4C) isinserted along the ipsilateral blade and advanced to position shim 132within the anterolateral region of the L5-S1 disc space. Referring toFIGS. 22 and 23A-23C, blades 120, 122 can each be provided with a slot133 for receiving a shim 132. FIG. 22 illustrates blade 122 with a shim132 in slot 133, while blade 120 of FIG. 22 is shown without a shim orother structure positioned within its respective slot 133.

Shim 132 is an elongated plate with a substantially planar proximalportion 130 a and a curved distal portion 130 b. The curved distalportion 130 b also tapers to a pointed distal tip 131 that is designedfor introduction into an intervertebral space. The substantially planarproximal portion of shim 132 has a height h greater than its thickness tto minimize obstruction of access to the disc space when the shim is inplace, and the height of the shim narrows anteriorly to pointed distaltip 131. Shim 132 further has a reversed curvature, in that its distalportion 130 b is curved away from ipsilateral retraction blade 122 andtoward contralateral retraction blade 120.

The curvature of the distal portion of shim 132 is relatively slight,being only 5-15 degrees out of the plane of the planar proximal portion130 a of shim 130. Alternatively, as shown in FIGS. 18A, 18B, and 18C,shim 132 can be substantially straight along its entire length. Shim 132is attached to ipsilateral blade 120 to help lock retractor instrument110 in position until removal of the instrument is desired, anddistracts the adjacent vertebral bodies (such as L5 and S1) to restoredisc height. Shim 132 can be coupled to ipsilateral blade 120 and/orcontralateral blade 122 in a variety of manners. In a preferredembodiment, shim 132 comprises a projecting portion 135 that projectsoutward from a surface of shim 132. Projecting portion 135 can be aspring-loaded member that is biased outward from the surface of shim132. In use, shim 132 can be positioned in a slot 133 and securedthereto to the respective blade (e.g., blade 122 in FIG. 23C).

As shown in FIGS. 21 and 23B, a plurality of spaced detents or openings137 can extend along the length of a rear side 139 of blade 122 toreceive projecting portion 135 and secure shim 132 to blade 122. Whenprojecting portion 135 is in a locked position (i.e., with projectingportion 135 extending at least partially through a detent 137), shim 132is restricted from moving relative to blade 122. To adjust the positionof shim 132 relative to blade 122, projecting portion 135 can be pushedinward towards the surface of shim 132, moving projecting portion 135out of detent 137 and releasing shim 132 from blade 122. Once projectingportion 135 is released from detent 137, shim 132 can be moved intoanother position along blade 122 by pushing or otherwise directing shim132 downward along the length of blade 122. This process can be repeateduntil shim 132 is secured to blade 122 in a desired position.

Shim 132 also rigidly couples ipsilateral retractor blade 122 in fixedrelation relative to the vertebral bodies, and helps ensure thatsurgical instruments employed within the operative corridor are notadvanced outside the operative corridor, thereby avoiding inadvertentcontact with the exiting nerve roots and vasculature during the surgery.Once the operative corridor is established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated within the operative corridor depending upon the givensurgical procedure.

Superior and inferior soft tissue retractors (not shown) may also beplaced as needed for retraction for any creeping retroperitonealcontents to allow creation of a box-type approach to the L5-S1 discspace. Discectomy is than carried out in a conventional fashion toevacuate as much of the disc and interspace contents as possible. Thehandle portion 112 may be coupled to any number of mechanisms forrigidly registering it in fixed relation to the operative site, such asthrough the use of an articulating arm mounted to the operating table22.

Introducer Instrument

Once the discectomy has been completed, trial implants are introducedinto the L5-S1 disc space 70 to select an appropriate size finalimplant, and a final implant is then introduced into the disc space.

FIGS. 6-9 illustrate an introducer instrument 140 for introducingimplants into the disc space. Instrument 140 includes a rigid sheath 142(FIGS. 6-7) that is sufficiently long to reach the L5-S1 disc space 70.A longitudinal axis 144 of sheath 142 is illustrated by a dashed line.Instrument 140 is provided with a proximal handle 146 that is coupled toa rotatable shaft 147 (FIG. 8) inside a ridged collar 148 (FIG. 7) sothat shaft 147 can be rotated within sheath 142 by rotating handle 146as collar 148 is grasped by the surgeon's hand to maintain collar 148stationary. As shown in FIG. 7, an externally threaded rod 150 projectsfrom a cylindrical distal tip 152 of sheath 142 along longitudinal axis144 on sheath 142. A pair of small coupling pins 154, 156, which aresmaller than threaded rod 150, project from distal tip 152 on eitherside of rod 150 in a fixed spaced alignment generally along a commonplane that bisects shaft 142 along its axis 144. Coupling pins 154, 156are substantially shorter and of much smaller diameter than the threadedrod 150. For example, coupling pins are less than 25% or even 10% of thediameter and length of threaded rod 150 projecting from the tip 152 ofinstrument 140.

As shown best in FIG. 8, threaded rod 150 is connected to rotatableshaft 147 by a reduced diameter step-down extension 158 that projectsout of distal tip 152 of sheath 142 to provide a gap between threadedrod 150 and the face 160 of distal tip 152. Distal tip 152 (and pins154, 156 that it carries) can be selectively advanced toward andretracted from implant 172 in a pathway generally parallel tolongitudinal axis 144 by rotating handle 146. As handle 146 rotatescounterclockwise, it drives shaft 147 to turn threaded rod 150 andloosen the connection between rod 150 and a threaded opening in theimplant. Since pins 154, 156 have a much shorter axial length thanthreaded rod 150, only slight loosening of the threaded rod is requiredto disengage pins 154, 156 from the implant. Once pins 154, 156 aredisengaged from the implant, they can be repositioned in another set ofopenings on the implant to change the angle between instrument 140 andthe implant. Handle 146 is then rotated clockwise to tighten the pins intheir new openings to fix the new angular relationship betweeninstrument 140 and the implant.

Threaded rod 150 and coupling pins 154, 156 form an example of a dockingelement of introducer instrument 140. The docking element selectivelydocks with an interface element 170 of an implant 172, as shown in FIG.9. The docking element docks at a plurality of positions with interfaceelement 170 to selectively alter an angle between implant 172 andintroducer instrument 140. Implant 172 has a pivot axis 174 around whichimplant 172 may be pivoted relative to longitudinal axis 144 ofinstrument 140.

An example of an implant 172 is shown in greater detail in FIGS. 10A and10B, where implant 172 has a top bearing face 176, a bottom bearing face178, a front face 180, a rear face 182, an ipsilateral face 184 and acontralateral face 186. A rotation pin 188 extends between top andbottom faces 176, 178 and rotates relative to implant 172; pivot axis174 of implant 172 extends along the axis of rotation pin 188. Interfaceelement 170 (FIGS. 9 and 10A) has a recessed slot 190 between top andbottom faces 176, 178 that provides access to the side of rotation pin188 in which an internally threaded opening 191 is provided which hasthreads that are complementary to the external threads of rod 150 ofintroducer instrument 140. An upper arcuate lip 192 and lower arcuatelip 194 form slot 190 cooperatively therebetween. Lips 192, 194 arespaced from and generally parallel to the outer walls of rotation pin188. Lips 192, 194 of interface element 170 each have a series of spaceddocking holes that form paired upper and lower sets of spaced holesarranged on the curved surfaces of the lips. These docking holes extendpartially circumferentially around pivot axis 174, and selected pairs ofspaced docking holes are positioned to mate with the docking element ofintroducer instrument 140. This docking is illustrated in greater detailin FIG. 9 wherein face 160 of distal tip 152 is curved to fit inregister with the curved faces of lips 192, 194 with pin 154 in an uppermember of a docking pair of holes on upper lip 192 and pin 156 (notshown in FIG. 9) in a corresponding aligned lower member of the dockingpair of holes on lower lip 194. Interface element 170 therefore includesspaced docking holes that extend partially circumferentially aroundpivot axis 174 so that selected pairs of docking holes are positioned tomate with the docking element of introducer instrument 140.

In use, introducer instrument 140 is secured to an implant 172 bythreading rod 150 into opening 191 of rotation pin 188 by rotatinghandle 146 to turn shaft 147 within sheath 142. Handle 146 is rotateduntil implant 172 is tightly secured to distal tip 152 and pins 154, 156are aligned with and inserted within a pair of the upper and loweraligned docking holes. The angular relationship between instrument 140and implant 172 can be altered by slightly unscrewing threaded rod 150from threaded opening 191. This action moves face 160 of distal tip 152sufficiently out of engagement with interface element 170 to disengagepins 154, 156 from a first set of docking holes without completelydisconnecting instrument 140 from implant 172. The implant 172 andinstrument 140 can then pivot relative to one another until sheath 142is again advanced to engage coupling pins 152, 154 with a new pair ofdocking holes by rotating handle 146 to once again securely engageinstrument 140 to implant 172, so that the implant is fixed at a newangular relationship with the instrument.

Although a particular embodiment of the device is illustrated in whichthe angular relationship between instrument 140 and implant 172 can beselectively altered, many other means for varying this angularrelationship to pivot the implant are contemplated. For example,rotation of handle 146 can actuate a gear that pivots implant 172, orhandle rotation can actuate a cam that selectively moves pins 154, 156to selectively engage and disengage them from interface element 170.Alternatively the tip of instrument 140 can fit into a slot withinimplant 172 to pivot the implant as instrument 140 is moved from thecontralateral to the ipsilateral arm of the retractor instrument. Inother embodiments, a universal joint is provided between the instrument140 and implant 172 to selectively pivot the implant relative to theinstrument. Different numbers and arrangements of the pins can also beprovided. Electronic devices can also be used that rotate the implant inthe plane of the disc space while maintaining the instrument within theoperative pathway defined between the retraction blades of instrument140.

The Implant

Additional features of implant 172 are shown in detail in FIGS. 10 and11 to illustrate details that make the implant particularly suitable forinsertion and progressive pivoting of the implant within the L5-S1 discspace, as described in greater detail below. The implant tapers inheight from the height h1 of front face 180 to height h2 of rear face182, and is elongated in a direction transverse to the direction oftapering height. Hence front face 180 and rear face 182 are longer thanipsilateral and contralateral faces 184, 186. The implant material ismade of a generally compressible or elastomeric material. Front face 180is generally convex, ipsilateral face 184 includes interface element170, rear face 176 is generally flat, and contralateral face 186 isrounded at its front and rear edges to minimize impact damage to spinalstructures as the implant is introduced into the disc space and pivotedinto position. Implant 172 is also partially hollow and may haveipsilateral and contralateral windows 200, 202 extending between top andbottom faces 176, 178. The windows are formed by an internal dividerwall 204 that extends from the front to rear of implant 172 andsubstantially bisects the implant into ipsilateral and contralateralhalves. However, ipsilateral window 200 is smaller than contralateralwindow 202 because a portion of the ipsilateral half of implant 172 isoccupied by rotation pin 188 and the structure that supports it. Thewindows 200, 202 provide communication between the open bottom and topfaces of the implant to promote ingrowth of tissue within and throughimplant 172.

Top and bottom faces 176, 178 are provided with protuberances 206 thatalso help promote bone growth into implant 172. The protuberances maytake a variety of shapes, but the illustrated frustopyramidalprotuberances 206 are believed to be particularly suitable for thispurpose.

In addition to the implant, trial spacers are also provided to helpassess the size of the disc space once the disc space contents have beenevacuated but before the final implant is advanced into the disc space.

FIGS. 11A, 11B, and 11C illustrate another embodiment of an implant 272.To facilitate comparison to implant 172, FIGS. 11A-C use referencenumbers with the same two final digits for elements that are generallysimilar to elements identified in FIGS. 10A and 10B. Thus, implant 272has a top bearing face 276, a bottom bearing face 278, a front face 280,a rear face 282, an ipsilateral face 284 and a contralateral face 286. Arotation pin 288 extends between top and bottom faces 276, 278 androtates relative to implant 272. Pivot axis 274 of implant 272 extendsalong the axis of rotation pin 288.

An interface element 270 (FIGS. 11B and 11C) has a recessed slot 290between top and bottom faces 276, 278 that provides access to the sideof rotation pin 288 in which an internally threaded opening 291 isprovided which has threads that are complementary to the externalthreads of rod 150 of introducer instrument 140. An upper arcuate lip292 and lower arcuate lip 294 form slot 290 cooperatively therebetween.For clarity, FIG. 11B is shown without pin 288 fitted or received inimplant 272.

Lips 292, 294 of interface element 270 can have a series of spaceddocking holes such as that shown in FIGS. 10A and 10B. Alternatively, asshown in FIGS. 11B and 11C, lips 292, 294 can be formed without suchdocking holes. Instead, the introducer instrument can be shaped tocontact a portion of the upper and/or lower curved faces of lips 292,294, thereby forming a frictional fit between the convex face of implant272 and a concave face 160 of the introducer instrument 140. Thus, inuse, introducer instrument 140 can be secured to implant 272 bythreading rod 150 into opening 291 of rotation pin 288 by rotatinghandle 146 to turn shaft 147 within sheath 142. When handle 146 isrotated a sufficient amount, implant 272 will be tightly secured to face160 of distal tip 152. The angular relationship between instrument 140and implant 272 can be altered by slightly unscrewing threaded rod 150from threaded opening 291. This action moves face 160 of distal tip 152sufficiently out of engagement of the frictional fit with interfaceelement 270 (or other contacting portion of a surface of implant 272).Implant 272 and instrument 140 can then pivot relative to one anotheruntil sheath 142 is again advanced to engage the instrument 140 andimplant 272 in a frictional fit that is tight enough to restrictrelative movement of the instrument 140 and implant 272.

As shown in FIGS. 11B and 11C, implant 272 can be constructed so that itis substantially the same thickness (height) along its length (FIG.11B), while at the same time varying in thickness (height) along itswidth (FIG. 11C). In particular, as shown in FIG. 11C, the thickness(height) of implant 272 can vary from a first larger height to a secondsmaller height to facilitate the implantation of the device in thepatient.

Like implant 172, implant 272 can be provided with protuberances 306that help promote bone growth into implant 172. As noted above, suchprotuberances can take a variety of shapes. Also like implant 172,implant 272 can be at least partially hollow and can have one or morewindows (e.g., windows 300, 302). Windows 300, 302 can provide the samebenefits as windows 200, 202 in the previous embodiment, which is toprovide communication between the open bottom and top faces of theimplant to promote ingrowth of tissue within and through implant 272.Implant 272 can also have one or more openings 303 that extend through aside wall of the implant to further promote ingrowth of tissue and tofacilitate access to internal areas of implant 272 (e.g., access to oneor both of windows 300, 302) when implant 272 is implanted in the body.

Windows 300, 302 can extend between top and bottom faces 276, 278 asshown in FIG. 11A. The windows can be formed by an internal divider wall304 that substantially bisect the implant into two halves. Unlikedivider wall 204 shown in FIG. 10A, however, divider wall 304 preferablyextends diagonally across implant 272 from an area adjacent or near thepin 288 to an area at or near contralateral face 286. By extendinggenerally diagonally across implant 272 as shown in FIG. 11A, diagonalwall 304 can provide structural strength to the implant in the generaldirection of the force that will be applied to implant 272 duringimplantation. For example, as shown in FIG. 20, divider wall 304 islocated substantially in-line with the instrument 140.

FIG. 12 illustrates another version of an implant 220. This implant issimilar to that shown in FIGS. 10-11, except it is substantiallyrectangular in shape instead of polygonal, and it has a rotation pin 222with a pivot axis 224 that extends between a front and rear face ofimplant 220. Rotation pin 222 includes an opening 226 (e.g., a threadedopening) for receiving a threaded distal end of introducer instrument140. As described above with respect to implant 172, implant 220 can besecured to threading rod 150 by positioning rod 150 into opening 226 androtating handle 146 to turn shaft 147 and tighten the distal end of theinstrument (e.g., face 160) to a facing surface of implant 220.

Because rotation pin 222 is positioned horizontally (FIG. 12) ratherthan vertically (FIG. 10A), implant 220 is therefore suitable forpivoting up and down with respect to introducer instrument 140 insteadof from side-to-side as with implant 172. It may also have varieddimensions medial to lateral as described for implant 172, althoughother embodiments do not taper and are of uniform height. The embodimentof the implant shown in FIG. 12 is generally used in surgeries superiorto the L5-S1 space, for example in the L4-L5 space or the L3-L4 space.By providing an implant that can pivot vertically, such as implant 220,the implantation site can be more easily accessed from an incision pointsuperior or inferior to the implantation site. For example, in use, theimplant can be delivered to the implantation site from a locationsuperior to iliac crest 30 and pivoted vertically into the desiredposition at the implantation site.

As with the other implants described herein, implant 220 can be providedwith one or more windows 228, 230 and a plurality of protrusions 232 topromote the ingrowth of tissue. Implant 220 can also be provided with aplurality of docking holes 234 to help lock or secure implant 220 to adistal end of instrument 140. Alternatively, implant 220 can be securedto the instrument 140 via a frictional fit or other similar mechanism.FIGS. 19A, 19B, and 19C illustrate another embodiment of an implant thatcan pivot up and down (e.g., vertically), in a manner similar to thatshown in FIG. 12. Implant 320 is configured to receive a rotation pin(not shown) in a recess 322 between a top surface 324 and a bottomsurface 326 of implant 320. As described in other embodiments, implant320 can include a plurality of windows 330, 332 separated by a dividerwall 334. In addition, openings 336 can be formed in the side of theimplant as shown in FIGS. 19A and 19B.

Introducing the Trial Spacer and Disc Implant

Once the operative corridor has been established by retractioninstrument 110 and the operative field has been exposed, a trial spacer210 is attached to introducer instrument 140 and advanced into the L5-S1disc space as shown in FIG. 13. The trial spacer is generally similar toimplant 174, except it does not have the protuberances projecting fromits top and bottom faces. For the initial introduction of trial spacer210, the spacer is directly laterally attached to instrument 110. Thedirect lateral attachment is shown in FIG. 13, wherein the longitudinalaxis of sheath 142 is generally parallel to flat rear face 182 ofimplant 210. Because of the anterolateral operative pathway to the discspace, trial implant 210 moves along a generally oblique or diagonalpathway into the disc space. The “oblique” pathway is one that travelsdiagonally within the body, for example in an oblique anatomic plane.The oblique pathway may be a diagonal pathway, for example between 15and 45 or 60 degrees to a coronal plane of the body. In FIG. 13, theoblique pathway is shown at an angle a of about 30 degrees to coronalplane 212 (FIG. 13). The oblique pathway may be either in a transverseplane of the body, or above or below a transverse plane (for examplebetween 15 and 45 or 60 degrees to a transverse plane of the body).However, in a particular disclosed embodiment of the method, fluoroscopyis used to detect the level of the target disc space (such as L5-S1) sothat the instrument, spacer and implant can be introduced diagonally inthe body, but generally in the plane of the L5-S1 disc space.

As trial spacer 210 enters the illustrated L5-S1 disc space (FIGS. 13and 14A), contralateral face 186 impacts the posterior contralateralaspect of the disc space. The rounded edges of contralateral face 186help avoid damage to the structures which the contralateral face 186 ofthe trial spacer encounters. The trial spacer is then progressivelyreoriented from its diagonal orientation in the disc space (FIG. 14A) toa generally medial-lateral orientation (FIG. 14C) by successivelyretracting sheath 142, pivoting the trial spacer on rotation pin 188 byforcing contralateral face of trial spacer 210 against the posterolateral apophyseal ring and moving introducer instrument 140 towardipsilateral retractor arm 118, and repositioning coupling pins in a newset of docking holes that maintain the trial spacer in an intermediateposition shown in FIG. 14B. Sheath 142 is then retracted again, and thetrial spacer pivoted on rotation pin 188 to the generally medial-lateralorientation (FIG. 14C). As the trial spacer 210 moves from its initialdiagonal to final medial-lateral orientation (with its flat rear facegenerally parallel to a coronal plane of the body), sheath 142 movesfrom a first position abutting contralateral retractor blade 120 (FIG.14A) to a second position abutting ipsilateral blade 122 (FIG. 14C).

Trial spacers of different sizes may be introduced into the disc spaceand pivoted from the diagonal to the medial-lateral orientation until atrial spacer of the appropriate size and height is found. Introducerinstrument 140 is detached from trial spacer 210 by rotating handle tounscrew threaded 150 from the internally threaded opening of trialspacer 210 to secure different trial spacers until the correct one isfound. The trial spacer is then withdrawn from the disc space anddetached from introducer instrument 140, and the final implant 172 isdirectly laterally attached to distal tip 152 of introducer instrument140 (as illustrated in FIG. 15) by rotating handle 146 to screw thethreaded rod at the tip of instrument 140 into the internally threadedhole on the implant. With the implant 172 directly laterally attached toinstrument 141, the elongated implant 172 can be introduced through arelatively narrow operative pathway between the arms of retractorinstrument 110. FIG. 16A illustrates the diagonal introduction ofimplant 172 into the disc space along the same pathway already describedfor trial spacer 210. The implant enters the disc space with its flatrear face 182 at an angle of about 15-45 degrees (for example 30degrees) to a coronal plane of the body. The implant is thenprogressively reoriented by retracting sheath 142, pivoting implant 172within the disc space, and advancing sheath 142 to reengage couplingpins 154, 156 within a new set of docking holes to hold implant 172 inthe intermediate orientation shown in FIG. 16B wherein the implant is atan angle of about 15 degrees to a coronal plane of the body. Implant 172can then be further reoriented in this fashion until sheath 142 contactsipsilateral arm 118 of retractor instrument 110 (FIG. 16C). Once implant172 can not be reoriented any further using the instrument, handle 146is rotated to completely disengage introducer instrument 140 fromimplant 172. Instrument 140 is then withdrawn from retractor instrument110.

Additional positioning of implant 172 can be achieved by pushing it withthe tip of instrument 140, or with other elongated instrumentsintroduced through retractor instrument 110. Retractor instrument 110can then be removed from the body by moving arms 116, 118 toward oneanother to reduce the width of instrument 110 then withdrawing it fromthe body. Normal closure of the surgical incisions on the body surfaceis then carried out.

FIG. 20 illustrates implant 272 secured to instrument 140 and beingdelivered to an implantation site. The method of delivering implant 272is substantially the same as the method of delivering implant 172, whichis described above and shown in FIGS. 15-17.

Implant 272 is desirably secured to the distal end of instrument 140 sothat divider wall 304 is generally in-line with axis 350 of instrument140. In this manner, implant 272 can exhibit increased strength toensure that it can withstand the impaction force, which is generallyapplied along the axis 350 to deliver implant 272 to the desiredlocation in the body.

The implants described herein can be coated with and/or impregnated withvarious elements to promote bone in-growth. In a preferred embodiment,stem cells can be delivered along with the implant (either deliveredinto openings in the implant or coated thereon) to improve andfacilitate bone in-growth. In view of the many possible embodiments towhich the principles of the disclosed invention may be applied, itshould be recognized that the illustrated embodiments are only preferredexamples of the invention and should not be taken as limiting the scopeof the invention. Rather, the scope of the invention is defined by thefollowing claims. We therefore claim as our invention all that comeswithin the scope and spirit of these claims

1-50. (canceled)
 51. A method of positioning a spinal implant into anintervertebral space of a subject, comprising: positioning the subjectin a right lateral decubitus position; creating an anterolateralincision; establishing an oblique operative corridor in the subjectextending from the subject's skin to a location proximate ananterolateral portion of an intervertebral space between the L5 and S1vertebrae, wherein establishing the oblique operative corridorcomprises: inserting a finger into the anterolateral incision; palpatingthe subject with the finger in the anterolateral incision; identifyingan iliac vessel of the subject; identifying the oblique operativecorridor to the intervertebral space between the L5 and S1 vertebrae;inserting a first retractor blade lateralizing a left common iliac veinand a left common iliac artery, the first retractor blade having adistal portion extending away from a central axis of the first retractorblade; and inserting a second retractor blade lateralizing a rightcommon iliac vein and a right common iliac artery, such that the obliqueoperative corridor is established; advancing the spinal implant at leastpartially into the intervertebral space between the L5 and S1 vertebraevia the oblique operative corridor.
 52. The method of claim 51, whereinadvancing the spinal implant to the intervertebral space comprisesorienting a longitudinal axis of the implant to be substantiallyparallel to the direction of advancement.
 53. The method of claim 52,wherein advancing the spinal implant to the intervertebral spacecomprises inserting the spinal implant at least partially into theintervertebral space in a first orientation such that the longitudinalaxis of the implant is oriented substantially parallel to ananterolateral direction.
 54. The method of claim 51, wherein advancingthe spinal implant to the intervertebral space comprises rotating thespinal implant at least partially within the intervertebral space. 55.The method of claim 54, wherein rotating the spinal implant at leastpartially within intervertebral space comprises rotating the spinalimplant to an orientation such that a longitudinal axis of the implantis oriented substantially parallel to the coronal plane of the subject.56. The method of claim 51, further comprising inserting a pin into atleast one of the first retractor blade or the second retractor blade.57. The method of claim 51, wherein the first retractor blade and thesecond retractor blade are disposed adjacent one another, wherein thefirst longitudinal axis is substantially parallel to the secondlongitudinal axis.
 58. The system of claim 51, wherein the secondretractor blade comprises a second distal portion, and the first distalportion extends beyond the second distal portion.
 59. The system ofclaim 58, wherein the second distal portion has a greatercross-sectional curvature and a greater longitudinal curvature than thefirst distal portion.
 60. A system for positioning a spinal implant intoan intervertebral space of a subject positioned in a right lateraldecubitus position, comprising: a first retractor blade configured tolateralize a left common iliac vein and a left common iliac artery wheninserted into an oblique operative corridor of the subject afterpalpating the subject with a finger in an anterolateral incision, theoblique operative corridor extending from the anterolateral incision inthe subject's skin to a location proximate an anterolateral portion ofan intervertebral space between the L5 and S1 vertebrae, the firstretractor blade having a first distal portion extending away from acentral axis of the first retractor blade; a second retractor bladeconfigured to lateralize a right common iliac vein and a right commoniliac artery when inserted into the oblique operative corridor of thesubject, such that the oblique operative corridor is established; and aspinal implant comprising an elongated body, the elongated bodycomprising: a front face defining a convex surface; a back face oppositethe front face; a top face defining a first set of protuberances; abottom face opposite the top face, the bottom face defining a second setof protuberances; an interface element extending between the front faceand the back face on a first side, wherein the interface element definesan upper lip along the top face and a lower lip along the bottom facewith a slot defined between the upper lip and the lower lip; and anaperture defined between the front face and the back face and extendingthrough the top face and the bottom face.
 61. The system of claim 60,wherein the interface element of the spinal implant comprises multiplepairs of spaced docking holes arranged on a curved surface that extendspartially circumferentially around a pivot axis.
 62. The system of claim60, wherein the first set of protuberances defined by the top face ofthe spinal implant are frustopyramidal.
 63. The system of claim 60,wherein the second set of protuberances defined by the bottom face ofthe spinal implant are frustopyramidal.
 64. The system of claim 60,wherein the back face of the spinal implant is substantially flat. 65.The system of claim 60, wherein the second retractor blade defines asecond central axis.
 66. The system of claim 65, wherein the firstretractor blade and the second retractor blade are disposed adjacent oneanother, wherein the first longitudinal axis is substantially parallelto the second longitudinal axis.
 67. The system of claim 65, wherein thesecond retractor blade comprises a second distal portion extending awayfrom the second central axis of the second retractor blade.
 68. Thesystem of claim 67, wherein the first distal portion extends beyond thesecond distal portion.
 69. The system of claim 67, wherein the seconddistal portion has a greater cross-sectional curvature and a greaterlongitudinal curvature than the first distal portion.
 70. The system ofclaim 60, wherein the spinal implant is rounded between the front faceand the back face.